Lubricant composition for preventing pre-ignition

ABSTRACT

The present invention relates to the use of a lubricant composition comprising (i) at least one dithiocarbamate compound; and (ii) at least one base oil, for preventing and/or reducing pre-ignition, in particular at low speed, in a vehicle engine, wherein said composition is applied during at least one change interval without the addition of a new lubricant composition, the content of dithiocarbamate compound being less than or equal to 1% by weight relative to the total weight of the lubricant composition.

TECHNICAL FIELD

The present invention relates to the field of lubricants, which may notably be used in vehicle engines, in particular lubricant compositions for preventing or reducing preignition in an engine.

Under ideal conditions, normal combustion in a spark ignition engine takes place when a mixture of combustible, and notably of fuel and air, is ignited in the combustion chamber inside the cylinder via the production of a spark coming from a spark plug. Such normal combustion is generally characterized by the expansion of the flame front through the combustion chamber in an ordered and controlled manner.

However, in certain cases, the air/fuel mixture may be prematurely ignited by a lighting source before the ignition by the spark from the spark plug, which leads to a phenomenon known as preignition.

Now, it is preferable to reduce or even eliminate preignition since this is generally reflected by the presence of a large increase in the temperatures and pressures in the combustion chamber, and thus have a significant negative impact on the efficiency and overall performance of an engine. Furthermore, preignition may cause significant damage to the cylinders, pistons, spark plugs and valves in the engine and in certain cases may even result in an engine breakdown, or even an engine failure.

More recently, low-speed preignition (LSPI) has been identified, notably by motor vehicle constructors, as a potential problem for downsized engines. LSPI generally takes place at low speeds and high loads and may lead to serious damage to the pistons and/or to the cylinders.

In addition, preventing and/or reducing preignition, in particular LSPI, must be maintained over time, i.e. during prolonged use of the lubricant composition, for example between two oil changes or after a certain number of kilometres driven.

Prior Art

Several theories have been put forward in an attempt to explain this complex phenomenon. It has notably been observed that the presence of small amounts of lubricant in the combustion chamber, mixing with the fuel, can aggravate preignition. Also, a link between the presence of a deposit in the combustion chamber and the occurrence of LSPI has been able to be established. Finally, the design of the engine itself may have an influence on preignition.

Thus, this phenomenon proves to be very complex and difficult to predict. As stated above, the nature of the lubricant contributes greatly thereto and lubricant compositions which can prevent or reduce the risk of preignition, in particular LSPI, have thus already been proposed.

Thus, patent application WO 2015/023559 describes a method for reducing preignition by adding, to a lubricant composition, an additive for retarding the ignition, said additive being chosen from organic compounds comprising at least one aromatic nucleus.

However, these light organic compounds might entail an excessive increase in the volatility of the lubricant.

It has thus also been proposed to add polyalkylene glycol, as is described in patent application WO 2017/021521, or alternatively to incorporate an organomolybdenum compound chosen from molybdenum dithiophosphates and sulfur-free molybdenum complexes, according to WO 2017/021523, in a lubricant composition so as to prevent or reduce preignition in an engine.

It is also known that the content of calcium-based detergent exerts strong leverage on triggering LSPI. Thus, it has been suggested to replace calcium-based detergents with magnesium-based detergents in lubricant compositions intended for reducing LSPI in vehicle engines.

The inventors have observed that preignition intensifies during prolonged use of the lubricant composition. Thus, preignition is particularly exacerbated in the case of “spent” lubricant compositions.

In particular, it has already been demonstrated that lubricant compositions which show a reduction in LSPI when they are fresh suffer degradation of their properties when they are spent, notably in the document “Low-speed preignition”, Engine Technology International, September 2018.

Finally, the solutions recommended in the prior art for fresh lubricant compositions prove to be insufficient in the case of spent compositions.

Moreover, the combination of at least one metallic molybdenum dithiocarbamate and of at least one methylene bis(dibutyldithiocarbamate) has already been described in patent application WO 2013/182581 for the purposes of preserving the fuel economy properties of a lubricant composition.

However, said document does not in any way suggest any effect of this combination, or of one of the additives taken in isolation, on the preignition that may arise in the engine.

The document Hong Liu et al., SAE International Journal of Fuels and Lubricants, 10(3), 2017 relates, for its part, to the development of low-viscosity gasoline engine oils for the purpose of improving the gasoline economy, but also for preventing LSPI preignition. However, said document does not at all mention a particular content of dithiocarbamate compound nor its specific value for preventing the preignition which takes place in engines.

For the purposes of the present invention, the term “spent lubricant composition” is intended to denote a lubricant composition used in the course of at least one oil change interval, i.e. over a distance travelled by the vehicle of between 10 000 and 30 000 km, preferably between 15 000 and 30 000 km.

The expressions “over the long term” or “in the long term” used according to the invention mean that the use of the lubricant composition extends to a spent lubricant composition.

For the purposes of the present invention, the term “fresh lubricant composition” is intended to denote a lubricant composition which has never been used in an engine.

For the purposes of the present invention, the term “aged lubricant composition” is intended to denote a lubricant composition which has undergone artificial aging, by simulation of the conditions of use of the lubricant composition in an engine. This artificial aging makes it possible to reproduce in an accelerated manner the aging of the oil when it is used in an engine in the course of an oil change interval. In particular, it is a lubricant composition which has undergone iron-catalyzed oxidation at a temperature above 150° C., preferably between 150° C. and 170° C. and for a time of at least 110 hours, preferably between 120 hours and 150 hours, according to the GFC Lu-43A-11 method.

All the embodiments defined according to the present invention for a spent lubricant composition are applicable to an aged lubricant composition.

As stated above, preignition has a tendency to become worse in the course of use of a lubricant composition, which is thus really efficient only when it is fresh. For obvious reasons, it is necessary to propose a solution for preventing preignition, which is long-lasting.

The need thus remains for lubricant compositions which have the capacity of preventing and/or reducing preignition, in particular LSPI, of an engine, in particular of a motor vehicle engine, in a prolonged manner in the course of its use, more precisely once the lubricant composition is spent.

The solutions favored in the prior art recommend selecting particular additives which can play a role in reducing the preignition which takes place in the engine. However, the lubricant compositions may incorporate a large number of different additives, giving them particularly advantageous properties, without it being possible to predict which additives will have a beneficial impact on preventing preignition, all the more so in the long term.

The need thus remains to propose additives which, when used in a lubricant composition, can prevent and/or reduce the preignition that may occur in the course of its prolonged use in an engine.

Finally, it is necessary to propose a solution for preventing preignition which does not require the addition of fresh lubricant composition to the engine in the course of its prolonged use, notably between the oil change intervals of the engine.

Thus, the need still remains to propose a lubricant composition for preventing and/or reducing preignition in the course of its use in an engine, which does not require the addition of lubricant composition between each engine oil change interval.

For obvious reasons, there is also a need to propose such lubricant compositions which show good stability, notably on storage.

The present invention is specifically directed toward meeting this need.

SUMMARY OF THE INVENTION

Thus, according to a first of its aspects, the present invention relates to the use of a lubricant composition comprising:

(i) at least one dithiocarbamate compound; and

(ii) at least one base oil;

for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle,

said composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition,

the content of dithiocarbamate compound being less than or equal to 1% by weight, relative to the total weight of the lubricant composition.

For the purposes of the present invention, the term “motor vehicle” is intended to denote a vehicle comprising at least one wheel, preferably at least two wheels, propelled by an engine, notably a combustion and explosion engine, in particular a reciprocating-piston or rotary-piston, diesel or positive-ignition internal combustion engine. Such engines may be, for example, two-stroke or four-stroke gasoline or diesel engines.

According to the invention, the prevention and/or reduction of preignition is preferentially measured for spent lubricant composition relative to fresh lubricant composition.

Contrary to all expectation, and as emerges from the examples given below, the inventors have demonstrated that the use of at least one dithiocarbamate compound in an aged lubricant composition can significantly improve the ignition temperature, in particular measured by high-pressure differential scanning calorimetry, of said composition and consequently retard the preignition, in particular LSPI, which may occur in the course of its use in an engine. The ignition temperature denotes here the temperature of initiation of the exothermic peak during a temperature rise, measured by HPDSC (High-Pressure Differential Scanning Calorimetry).

This result is all the more surprising with regard to the teaching of the document “Low-speed preignition”, Engine Technology International, September 2018, according to which an oil comprising a molybdenum dialkyldithiocarbamate undergoes a reduction in its LSPI properties when said oil is spent.

The dithiocarbamate compounds present in a lubricant composition according to the invention thus advantageously make it possible to prevent preignition, in particular LSPI, during its use in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km.

As a result, it is not necessary to renew the lubricant composition in the course of its use, for example between two engine oil changes, in order to conserve efficient prevention and/or reduction of preignition, in particular of low-speed preignition.

Moreover, the inventors have found, surprisingly, that the use of the dithiocarbamate compound in a content of less than or equal to 1% by weight in a lubricant composition used according to the invention also makes it possible to preserve satisfactory stability, in particular on storage, of said composition.

The stability on storage may be evaluated visually by rating the appearance of the lubricant composition and of the deposits formed during the storage of said composition, over a period generally ranging from 1 day to 3 months, and at different temperatures, typically at 0° C., at ambient temperature and at 60° C.

According to another of its aspects, a subject of the invention is also the use of at least one dithiocarbamate compound, in particular as defined below, in a lubricant composition comprising at least one base oil, for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle, said lubricant composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

According to another of its aspects, a subject of the invention is also the use of at least one dithiocarbamate compound, in particular as defined below, in a lubricant composition comprising at least one base oil, for limiting the degradation of the performance in terms of preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle, of said composition after its use in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

A subject of the invention is also a process for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle, preferably in the long term, comprising at least the following steps:

a) placing the engine in contact with a lubricant composition comprising at least one base oil and at least one dithiocarbamate compound, said dithiocarbamate compound being present in a content of less than or equal to 1% by weight, relative to the total weight of the lubricant composition;

b) running the engine in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

The invention also relates to the use of a lubricant composition comprising:

(i) at least one dithiocarbamate compound; and

(ii) at least one base oil;

for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle,

said composition having undergone iron-catalyzed oxidation at a temperature above 150° C., preferably between 150° C. and 170° C. and for a time of at least 110 hours, preferably between 120 hours and 150 hours, according to the GFC Lu-43A-11 method,

the content of dithiocarbamate compound preferably being less than or equal to 1% by weight, relative to the total weight of the lubricant composition.

DETAILED DESCRIPTION

Composition

Dithiocarbamate Compound

As mentioned above, a lubricant composition used according to the present invention comprises (i) at least one dithiocarbamate compound.

The dithiocarbamate compound may notably be chosen from metal dithiocarbamates, bisdithiocarbamates and mixtures thereof.

The metal dithiocarbamates may more particularly be defined according to the general formula (I) below:

in which the groups R₁ and R₂ represent, independently of each other, optionally substituted hydrocarbon-based groups, comprising from 1 to 30 carbon atoms, preferably from 4 to 18 carbon atoms, M represents a metal cation and n is the valency of this metal cation.

Preferably, M is molybdenum.

The metal dithiocarbamates that may be used according to the present invention are compounds that are well known to those skilled in the art and may be obtained via any process also known to those skilled in the art. An example of a process for preparing these compounds is notably described in U.S. Pat. No. 2,492,314.

Metal dithiocarbamates are notably known for their use in lubricant compositions as friction-modifying additives.

The MoDTC compound used according to the invention may be chosen from compounds in which the nucleus comprises two molybdenum atoms (dimeric MoDTC) and compounds in which the nucleus comprises three molybdenum atoms (trimeric MoDTC).

The trimeric MoDTC compounds are generally of formula Mo₃S_(k)L_(m) in which:

k is an integer at least equal to 4, preferably ranging from 4 to 10, advantageously from 4 to 7;

m is an integer ranging from 1 to 4; and

L is an alkyl dithiocarbamate group comprising from 1 to 100 carbon atoms, preferably from 1 to 40 carbon atoms, and advantageously from 3 to 20 carbon atoms.

Examples of trimeric MoDTC compounds that may be mentioned include the compounds and the processes for preparing same described in patent application WO 98/26030.

An example of a trimeric MoDTC compound is the one sold under the name Infineum® C9455B by the company Infineum International Ltd.

Preferably, the MoDTC compound used in the lubricant composition used according to the invention is a dimeric MoDTC compound. Examples of dimeric MoDTC compounds that may be mentioned include the compounds and the processes for preparing same described in patent EP 0 757 093.

According to a particular embodiment of the invention, the metal dithiocarbamate compound is a molybdenum dithiocarbamate (MoDTC) of formula (Ia) below:

in which the groups R₁ and R₂ are, independently of each other, as defined above,

X¹, X², X³ and X⁴, which may be identical or different, independently represent an oxygen atom or a sulfur atom.

Advantageously, X¹ and X² may represent an oxygen atom and X³ and X⁴ may represent a sulfur atom.

Advantageously, the MoDTC compound is chosen from the compounds of formula (Ia) in which:

X¹ and X² represent a hydrogen atom,

X³ and X⁴ represent a sulfur atom,

R₁ represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms,

R₂ represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms.

Thus, advantageously, the MoDTC compound may be chosen from the compounds of formula (Ia′):

in which R₁ and R₂ are as defined for formula (I) above.

As particular examples of MoDTC compounds, mention may be made of the products Molyvan L®, Molyvan 807® or Molyvan 822® sold by the company R.T. Vanderbilt Company or the products Sakuralube 200®, Sakuralube 165®, Sakuralube 525® or Sakuralube 600® sold by the company Adeka.

The lubricant composition used according to the invention may also be used with an organomolybdenum compound chosen from the MoDTC compounds described in patent application WO 2012/141855.

The bisdithiocarbamates may more particularly be defined according to the general formula (II) below:

in which:

-   -   the groups R₃ and R₄ represent, independently of each other,         optionally substituted hydrocarbon-based groups, comprising from         1 to 30 carbon atoms, preferably from 2 to 24 carbon atoms, more         preferentially from 3 to 8 carbon atoms; and     -   the groups R₅ represent a hydrocarbon-based group comprising         from 1 to 8 carbon atoms, preferably from 1 to 4 carbon atoms.

The bisdithiocarbamate compounds that may be used according to the present invention are compounds that are well known to those skilled in the art and may be obtained via any process also known to those skilled in the art.

Bisdithiocarbamates are notably known for their use in lubricant compositions as antioxidant additives.

This compound may advantageously be methylene bis(dibutyldithiocarbamate).

Examples of commercial products that may be mentioned include

Vanlube® 7723 sold by the company Vanderbilt or Additin® RC 6340 sold by the company Rhein Chemie.

According to one embodiment, a lubricant composition used according to the present invention comprises a mixture of at least one metal dithiocarbamate and of at least one bisdithiocarbamate, in particular as defined above.

Thus, the dithiocarbamate compound used in a composition according to the invention may be chosen more particularly from molybdenum dithiocarbamate (MoDTC), methylene bis(dibutyldithiocarbamate) (mDTC), and mixtures thereof.

The dithiocarbamate compound is present in a lubricant composition used according to the invention in a content of less than or equal to 1% by weight, relative to the total weight of the composition.

In particular, the dithiocarbamate compound may be present in a lubricant composition used according to the invention in a content strictly greater than 0.01% by weight, in particular in a content ranging from 0.02% to 1% by weight, preferably from 0.05% to 0.7% by weight, more preferentially from 0.1% to 0.5% by weight, relative to the total weight of the composition.

When the dithiocarbamate compound is present in a lubricant composition used according to the invention in a content of greater than 0.01% by weight, relative to the total weight of the composition, the ignition temperature, in particular measured by high-pressure differential scanning calorimetry, is higher than that observed for contents of less than 0.01% by weight.

Consequently, a composition comprising a content of greater than 0.01% by weight of dithiocarbamate compound, relative to the total weight of the composition, makes it possible to retard in a more pronounced manner the preignition, in particular LSPI, that may occur during its use in an engine.

Base Oil

As stated previously, a lubricant composition used according to the present invention comprises (ii) at least one base oil.

The base oil(s) may be oils of mineral, synthetic or natural, animal or plant origin, known to those skilled in the art.

In particular, the mineral or synthetic oils generally used in the lubricant composition belong to one of the groups I to V according to the classes defined in the API classification (or the equivalents thereof according to the ATIEL classification) as summarized in Table 1 below.

The API classification is defined in American Petroleum Institute 1509 “Engine Oil Licensing and Certification System” 17th edition, September 2012.

The ATIEL classification is defined in “The ATIEL Code of Practice”, number 18, November 2012.

TABLE 1 Content of Sulfur Viscosity saturates content index Group I  <90% >0.03% 80 ≤ VI < 120 Mineral oils Group II ≥90% ≤0.03% 80 ≤ VI < 120 Hydrocracked oils Group III ≥90% ≤0.03% ≥120 Hydrocracked or hydroisomerized oils Group IV PAO (poly-alpha-olefins) Group V Esters and other bases not included in groups I to IV

There is generally no limit as regards the use of different base oils for preparing a lubricant composition used according to the invention, apart from the fact that they must have properties, notably in terms of viscosity, viscosity index, sulfur content or resistance to oxidation, that are suitable for use in engines, in particular vehicle engines.

The mineral base oils include any type of base obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent deparaffinning, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

The synthetic base oils may be chosen from esters, silicones, glycols, polybutene, poly-alpha-olefins (PAO), alkylbenzene or alkylnaphthalene.

The base oils may also be oils of natural origin, for example esters of alcohols and of carboxylic acids, which may be obtained from natural resources, such as sunflower oil, rapeseed oil, palm oil, soybean oil, etc.

The base oil may be chosen more particularly from synthetic oils, mineral oils and mixtures thereof.

According to one embodiment, a lubricant composition used according to the present invention comprises at least one base oil chosen from the oils of group III, the oils of group IV and mixtures thereof.

Additives

A composition used according to the present invention may also comprise one or more additives as defined more precisely in the text hereinbelow, different from the dithiocarbamate compound defined above.

The additives that may be incorporated into a composition according to the invention may be chosen from antioxidants other than the bisdithiocarbamate compound defined above, detergents, viscosity index improvers, friction modifiers other than the metal dithiocarbamate compound defined above, wear-resistance additives, extreme-pressure additives, dispersants, pour point improvers, antifoams, and mixtures thereof.

It is understood that the nature of the additives used are chosen so as not to affect the properties of the lubricant composition, in particular as regards preventing and/or reducing preignition, notably LSPI, in an engine.

These additives may be introduced individually and/or in the form of a mixture such as those already available for sale for commercial lubricant formulations for vehicle engines, with a performance level as defined by the ACEA (Association des Constructeurs Européens d'Automobiles) and/or the API (American Petroleum Institute), which are well known to those skilled in the art.

According to a particular embodiment, a composition used according to the invention may also comprise at least one antioxidant additive, which is more particularly different from the bisdithiocarbamate compound defined above.

The antioxidant additive generally makes it possible to retard the degradation of the composition in service. This degradation may notably be reflected by the formation of deposits, the presence of sludges, or an increase in the viscosity of the composition. The antioxidant additives notably act as free-radical inhibitors or hydroperoxide destroyers.

Among the commonly used antioxidant additives, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type and phospho-sulfur-based antioxidant additives. Some of these antioxidant additives, for example the phospho-sulfur-based antioxidant additives, may be ash generators. The phenolic antioxidants additives may be ash-free or may be in the form of neutral or basic metal salts.

The antioxidants additives may notably be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C1-C12 alkyl group, N,N′-dialkyl-aryl-diamines, and mixtures thereof.

Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group, in which at least one carbon vicinal to the carbon bearing the alcohol function is substituted with at least one C₁-C₁₀ alkyl group, preferably a C₁-C₆ alkyl group, preferably a C₄ alkyl group, preferably with a tert-butyl group.

Amine compounds are another class of antioxidant additives that may be used, optionally in combination with the phenolic antioxidants additives.

Examples of amine compounds are aromatic amines, for example the aromatic amines of formula NR⁴R⁵R⁶ in which R₄ represents an optionally substituted aliphatic or aromatic group, R⁵ represents an optionally substituted aromatic group, R⁶ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R⁷S(O)_(z)R⁸ in which R⁷ represents an alkylene group or an alkenylene group, R⁸ represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulfurized alkylphenols or the alkali metal or alkaline-earth metal salts thereof may also be used as antioxidant additives.

Another class of antioxidant additives is that of copper compounds, for example copper thio- or dithio-phosphates, copper salts of carboxylic acids, and copper dithiocarbamates, sulfonates, phenates and acetylacetonates. Copper I and II salts and succinic acid or anhydride salts may also be used.

A composition used according to the invention may contain any type of antioxidant additive known to those skilled in the art.

Advantageously, a composition used according to the invention comprises at least one antioxidant additive chosen from diphenylamine, phenols, phenol esters and mixtures thereof.

A composition used according to the invention may comprise from 0.05% to 2% by weight and preferably from 0.5% to 1% by weight of at least one antioxidant additive relative to the total weight of the composition.

According to another embodiment, a composition used according to the invention may also comprise at least one detergent additive.

The detergent additives generally make it possible to reduce the formation of deposits on the surface of metal parts by dissolving the oxidation and combustion byproducts.

The detergent additives that may be used in a composition used according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon-based chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or an alkaline-earth metal.

The detergent additives are preferentially chosen from alkali metal or alkaline-earth metal salts of carboxylic acids, sulfonates, salicylates and naphthanates, and also phenate salts. The alkali metals and alkaline-earth metals are preferentially calcium, magnesium, sodium or barium.

These metal salts generally comprise the metal in a stoichiometric amount or in excess, thus in an amount greater than the stoichiometric amount. They are then overbased detergent additives; the excess metal giving the overbased nature to the detergent additive is then generally in the form of a metal salt that is insoluble in the oil, for example a carbonate, a hydroxide, an oxalate, an acetate or a glutamate, preferentially a carbonate. A composition used according to the invention may contain any type of detergent additive known to those skilled in the art.

Advantageously, a composition used according to the invention comprises at least one detergent additive chosen from alkaline-earth metal salts, preferably from calcium salts, magnesium salts, and mixtures thereof.

In particular, when the detergent is chosen from alkaline-earth metal salts, the detergent additive may be added to the composition so as to supply a content of metal element ranging from 150 ppm to 2000 ppm, preferably from 250 ppm to 1500 ppm.

According to yet another embodiment, a composition used according to the present invention may also comprise a viscosity index-enhancing additive.

As examples of viscosity index-enhancing additives, mention may be made of polymeric esters, hydrogenated or non-hydrogenated homopolymers or copolymers, styrene, butadiene and isoprene, polyacrylates, polymethacrylates (PMA) or olefin copolymers, notably ethylene/propylene copolymers.

Advantageously, a composition used according to the invention comprises at least one viscosity index-enhancing additive chosen from hydrogenated or non-hydrogenated homopolymers or copolymers, styrene, butadiene and isoprene. Preferably, it is a hydrogenated styrene/isoprene copolymer.

A composition used according to the invention may comprise, for example, from 2% to 15% by weight of viscosity index-enhancing additive relative to the total weight of the composition.

The wear-resistance additives and the extreme-pressure additives protect the friction surfaces by forming a protective film adsorbed onto these surfaces.

A wide variety of wear-resistance additives exists. Preferably, for the lubricant composition according to the invention, the wear-resistance additives are chosen from phospho-sulfur-based additives, such as metal alkylthiophosphates, in particular zinc alkylthiophosphates and more specifically zinc dialkyldithiophosphates or ZnDTP. The preferred compounds are of formula Zn((SP(S)(OR²XOR³))₂, in which R² and R³, which may be identical or different, independently represent an alkyl group, preferentially an alkyl group including from 1 to 18 carbon atoms.

Amine phosphates are also wear-resistance additives that may be employed in a composition according to the invention. However, the phosphorus introduced by these additives may act as a poison for the catalytic systems of motor vehicles since these additives are ash generators. These effects can be minimized by partially replacing the amine phosphates with additives which do not introduce phosphorus, for instance polysulfides, notably sulfur-based olefins.

A composition used according to the invention may comprise from 0.01% to 6% by weight, preferentially from 0.05% to 4% by weight and more preferentially from 0.1% to 2% of wear-resistance additives and of extreme-pressure additives, by weight relative to the total weight of the composition.

A composition used according to the invention is preferably free of wear-resistance additives and of extreme-pressure additives. In particular, a composition used according to the invention may be free of phosphate-based additives.

A composition used according to the invention may comprise at least one friction-modifying additive, which is more particularly different from the metal dithiocarbamate compound defined above. The friction-modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds providing metal elements, mention may be made of complexes of transition metals such as Mo, Sb, Sn, Fe, Cu or Zn, the ligands of which may be hydrocarbon-based compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms. The ash-free friction-modifying additives are generally of organic origin and may be chosen from fatty acid monoesters of polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides, fatty amines or fatty acid esters of glycerol. According to the invention, the fatty compounds comprise at least one hydrocarbon-based group comprising from 10 to 24 carbon atoms.

A composition used according to the invention may comprise from 0.01% to 2% by weight or from 0.01% to 5% by weight, preferentially from 0.1% to 1.5% by weight or from 0.1% to 2% by weight of friction-modifying additive, relative to the total weight of the composition.

Advantageously, a composition used according to the invention is free of friction-modifying additive different from the metal dithiocarbamate compound defined above.

A composition used according to the invention may also comprise at least one pour-point depressant additive.

By slowing down the formation of paraffin crystals, the pour-point depressant additives generally improve the cold-temperature behavior of the composition.

Examples of pour-point depressant additives that may be mentioned include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and polyalkylstyrenes.

Also, a composition used according to the invention may comprise at least one dispersant.

The dispersant may be chosen from Mannich bases, succinimides and derivatives thereof.

A composition used according to the invention may comprise, for example, from 0.2% to 10% by weight of dispersant relative to the total weight of the composition.

Applications

A lubricant composition according to the invention is more particularly intended to be used in an engine, notably in a vehicle engine, in particular in a gasoline vehicle engine.

It thus advantageously has properties, notably in terms of viscosity, viscosity index, sulfur content and oxidation resistance, which are suitable for use in engines, in particular vehicle engines.

Thus, preferably, a lubricant composition has a kinematic viscosity, measured at 100° C. according to the standard ISO 3104, of between 5 and 20 mm²/s, preferably between 5 and 15 mm²/s and more particularly between 6 and 13 mm²/s.

As indicated previously, a composition as described previously is advantageous in that it can, by means of its use in an engine, prevent and/or reduce the preignition which takes place in said engine over the long term, notably after use for a period corresponding to at least one oil change interval.

Thus, the invention relates to the use of a composition as defined previously for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle, said composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

In particular, preignition was observed at low speed in engines (LSPI) and is further exacerbated in direct-injection engines, in particular downsized engines.

Thus, the present patent application also relates to the use of a lubricant composition comprising:

(i) at least one dithiocarbamate compound; and

(ii) at least one base oil;

for preventing and/or reducing low-speed preignition (LSPI), in a vehicle engine, preferably of a motor vehicle, said composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

Particularly surprisingly, the inventors have found that the presence of a dithiocarbamate compound in an aged lubricant composition makes it possible to significantly reduce the occurrence of preignition in an engine.

Thus, the present invention also relates to the use of at least one dithiocarbamate compound, in particular as defined above, in a lubricant composition comprising at least one base oil, said lubricant composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition, for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle.

As demonstrated in the examples below, the selection of a particular additive, namely a dithiocarbamate compound, made it possible to propose a lubricant composition for preventing and/or reducing the preignition which may occur in the course of its prolonged use in an engine, without adding fresh lubricant composition.

Thus, still as demonstrated in the examples, a lubricant composition according to the invention has an ignition temperature higher than that obtained for a lubricant composition not comprising any dithiocarbamate compound or comprising an additional additive different from the dithiocarbamate required according to the invention.

In other words, the nature of the dithiocarbamate additive was not clearly deducible from its functions that may have been known previously.

The composition defined above thus has the advantage of preventing and/or reducing preignition in an engine, by virtue of its prolonged use in an engine.

Thus, the invention also relates to a process for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle, preferably in the long term, comprising at least the following steps:

a) placing the engine in contact with a lubricant composition comprising at least one base oil and at least one dithiocarbamate compound, said dithiocarbamate compound being present in a content of less than or equal to 1% by weight, relative to the total weight of the lubricant composition;

b) running the engine in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

As stated above, a spent lubricant composition used according to the invention has an ignition temperature higher than that of a spent lubricant composition not in accordance with this definition.

In particular, the temperature increase is at least 2%, preferably at least 4%, more preferentially at least 5%, measured according to the protocol detailed in the examples, relative to the ignition temperature of a lubricant composition comprising a base oil but free of dithiocarbamate compound. The ignition temperature corresponds to the temperature at and above which an exothermic reaction is initiated.

Thus, the invention also relates to the use of at least one dithiocarbamate compound, in particular as defined above, for the purposes of increasing the ignition temperature, measured by high-pressure differential scanning calorimetry, of a lubricant composition, in particular by at least 2%, preferably by at least 4%, said composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition, relative to a spent lubricant composition free of any dithiocarbamate compound.

According to the invention, the particular, advantageous or preferred features of the composition according to the invention make it possible to define uses according to the invention that are also particular, advantageous or preferred.

Throughout the description, including the claims, the expression “including a” should be understood as being synonymous with “including at least one”, unless otherwise specified.

The terms “between . . . and . . . ”, “comprises from . . . to . . . ”, “formed from . . . to . . . ” and “ranging from . . . to . . . ” should be understood as being limits inclusive, unless otherwise mentioned.

In the description and the examples, unless otherwise indicated, the percentages are weight percentages. The percentages are thus expressed are as weight percentages relative to the total weight of the composition. The temperature is expressed in degrees Celsius unless otherwise indicated, and the pressure is atmospheric pressure, unless otherwise indicated.

The invention will now be described by means of the examples that follow, which are, needless to say, given as nonlimiting illustrations of the invention.

Examples

Methods

Method for Aging the Lubricant Oils

The oils used in the examples below underwent simulated aging. This simulation is performed by oxidation of the oil catalyzed with 100 ppm of iron at 170° C. for 144 hours, according to the GFC-Lu-43A-11 method.

Laboratory Measurement of the Preignition Tendency

In the examples detailed below, the preignition tendency is determined in terms of temperature of initiation of the exothermic reaction, measured by HPDSC (High-Pressure Differential Scanning Calorimetry).

This measurement is performed using a Mettler-Toledo LG3300 machine according to the protocol detailed below:

-   -   2±0.05 mg of sample to be analyzed are weighed out in a tank;     -   The open sample and the reference are placed on the surface of         the detector;     -   The cell is closed hermetically and mechanically;     -   A pressure of between 1 and 20 bar is applied to the cell;     -   The temperature of the sample is equilibrated at the measurement         starting temperature, between 20° C. and 80° C., preferably         between 30° C. and 70° C., maintained for 1 to 15 minutes,         preferably for 2 to 10 minutes;     -   At least one temperature ramp is applied to the sample, between         the starting temperature and a temperature of between 100° C.         and 400° C., preferably between 150° C. and 350° C., more         preferentially between 200° C. and 300° C.

Software, such as the STARe software, makes it possible to visualize the differences in heat exchange between the sample and the reference.

The temperature of appearance of an exotherm on the curve thus obtained is likened to the phenomenon of preignition, such as LSPI.

This temperature is correlated to the time. Thus, the higher it is, the more the preignition will be retarded in the combustion chamber in the course of the use of the composition.

Measurement of the Stability

The stability of the compositions is evaluated by rating the change in their appearance after storage at different temperatures.

After preparation of the lubricant composition, three samples are distributed in test tubes, which are then closed.

The test tubes are stored for 3 months under the following conditions:

-   -   one tube stored in a chamber thermostatically maintained at         about 60° C.,     -   one tube at stored at ambient temperature;     -   one tube stored in a refrigerated cabinet at about 0° C.

In the course of the first month, the ratings are made on the first day, the third day and then once a week, and subsequently once every two weeks. The samples achieving a rating of 5 are discarded, even before the end of the three months of storage.

The rating is performed according to three criteria:

-   -   the clarity: the test tube is visualized as it is;     -   the general evaluation of the deposits: the test tube is         upturned and the deposits are evaluated; and     -   the form of the deposits.

According to the form of the deposit, it is also possible to determine the diameter (D) and/or the thickness (E) of the deposit (in mm).

As a function of the rating results obtained for each of these three criteria, the composition is defined as being stable or unstable.

Example 1: Preparation of the Lubricant Compositions

The lubricant compositions A0 to A4 were prepared.

Their kinematic viscosity at 100° C. was determined according to the standard ISO 3104 and their properties in terms of predisposition to self-ignition were measured.

The details of the compositions are presented in Table 2 below, in which the proportions of the various compounds are indicated as mass percentages.

TABLE 2 Composition A0 A1 A2 A3 A4 Base oil Group III/IV 72.8 72.3 72.6 72.7 71.8 Additive package* 16.7 16.7 16.7 16.7 16.7 Viscosity index enhancer of 10.5 10.5 10.5 10.5 10.5 hydrogenated styrene/isoprene copolymer type MoDTC (Sakuralube ® 525 from 0 0.5 0.2 0.1 0 Adeka) mDTC (Vanlube ® 7723 from 0 0 0 0 1 Vanderbilt) KV100 (mm²/s) 11.52 11.46 11.51 11.47 11.46 *The additive package is a mixture of different additives that are common in the field of lubricants and commercially available. It comprises wear-resistance additives of zinc dithiophosphate type, detergents based on calcium and magnesium, and dispersants of PIBSI type. In each of the compositions thus prepared, the amount of calcium is 1350 ppm by weight and the amount of magnesium is 300 ppm by weight.

The compositions are prepared by mixing, at a temperature of the order of 30 to 40° C., of the compounds detailed in Table 2.

The lubricant compositions thus prepared have kinematic viscosity values at 100° C. that are suitable for their use in engines, in particular vehicle engines.

The lubricant compositions are subsequently aged according to the protocol (aging method) detailed above.

Example 2: Evaluation of the LSPI Performance of the Lubricant Compositions

The exothermic reaction initiation temperature (ignition temperature) was measured for each of the lubricant compositions of Example 1, according to the measurement method (laboratory preignition tendency method) defined above.

The results are given in Table 3 below.

TABLE 3 Composition Ignition temperature [° C.] A0 (Reference) 196 A1 (Invention) 210 A2 (Invention) 211 A3 (Invention) 210 A4 (Invention) 214

Compositions A1 to A4 according to the invention, comprising molybdenum dithiocarbamate or methylene bis(dibutyldithiocarbamate), have higher ignition temperatures than for the same composition not comprising any dithiocarbamate compound required according to the invention (reference composition A0).

These measurements thus make it possible to demonstrate that the addition of at least one dithiocarbamate compound to an aged lubricant composition makes it possible to significantly retard preignition, in particular LSPI, in the course of its use in an engine, under conditions simulating aging of the lubricant composition.

In the examples that follow, the lubricant compositions are prepared and tested in comparison with a reference lubricant composition not comprising any dithiocarbamate compound.

For this reference composition, the kinematic viscosity at 100° C. was determined according to the standard ISO 3104. The composition was subsequently aged according to the catalyzed aging protocol described above. Finally, the exothermic reaction initiation temperature (ignition temperature) was measured, according to the measurement method (laboratory preignition tendency method) defined above.

The details of the reference composition (mass percentages) and the results obtained are presented in Table 4 below.

TABLE 4 Composition Reference Base oil Group III/IV 72.8 Additive package* 15.7 Viscosity index enhancer of hydrogenated 10.5 styrene/isoprene copolymer type Viscosity index enhancer of polymethacrylate type 0.2 Diphenylamine antioxidant (Irganox ® L-57) 0.8 KV100 (mm²/s) 11.51 Ignition temperature (° C.) 197 *The additive package is a mixture of different additives that are common in the field of lubricants and commercially available. It comprises wear-resistance additives of zinc dithiophosphate type, detergents based on calcium and magnesium, and dispersants of PIBSI type.

Example 3: Preparation of the Lubricant Compositions

The lubricant compositions B0 to B7 were prepared.

In particular, composition B0 is outside the invention since it comprises a content of dithiocarbamate compound of greater than 1% by weight.

Compositions B1 to B7 are in accordance with the invention.

Their kinematic viscosity at 100° C. was determined according to the standard ISO 3104.

The details of the compositions are presented in Table 5 below, in which the proportions of the various compounds are indicated as mass percentages.

TABLE 5 Composition B0 B1 B2 B3 B4 B5 B6 B7 Base oil 71.3 72.3 72.6 72.7 72.725 72.75 72.775 72.79 Group III/IV Additive 15.7 15.7 15.7 15.7 15.7 15.7 15.7 15.7 package* Viscosity index 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 enhancer of hydrogenated styrene/isoprene copolymer type Diphenylamine 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 antioxidant (Irganox ® L-57) Polymethacrylate 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 MoDTC 1.5 0.5 0.2 0.1 0.075 0.05 0.025 0.01 (Sakuralube ® 525 from Adeka) KV100 (mm²/s) 11.77 11.46 11.51 11.48 11.48 11.48 11.38 11.49 *The additive package is a mixture of different additives that are common in the field of lubricants and commercially available. It comprises wear-resistance additives of zinc dithiophosphate type, detergents based on calcium and magnesium, and dispersants of PIBSI type.

The compositions are prepared by mixing, at a temperature of the order of 30 to 40° C., of the compounds detailed in Table 5.

The lubricant compositions thus prepared have kinematic viscosity values at 100° C. that are suitable for their use in engines, in particular vehicle engines.

The lubricant compositions are subsequently aged according to the protocol (aging method) detailed above.

Example 4: Evaluation of the Performance of the Lubricant Compositions

The exothermic reaction initiation temperature (ignition temperature) was measured for each of the lubricant compositions of Example 3, according to the measurement method (laboratory preignition tendency method) defined above.

The stability of each of the lubricant compositions was also evaluated according to the protocol (stability measurement) defined above.

The results are given in Table 6 below.

TABLE 6 Ignition Composition temperature [° C.] Stability B0 (outside the invention) N/A Poor stability B1 (Invention) 208 Good stability B2 (Invention) 211 Good stability B3 (Invention) 210 Good stability B4 (Invention) 208 Good stability B5 (Invention) 210 Good stability B6 (Invention) 209 Good stability B7 (Invention) 206 Good stability

Compositions B1 to B7 according to the invention, comprising molybdenum dithiocarbamate in a content of less than or equal to 1% by weight, have good stability, in contrast with composition B0 which has a poor stability rating with the appearance of cloudiness.

These measurements thus make it possible to demonstrate that the addition of at least one dithiocarbamate compound to an aged lubricant composition, in a content not exceeding 1% by weight, makes it possible to obtain a lubricant composition which remains stable over time.

Moreover, compositions B1 to B7 all have ignition temperatures that are higher than that obtained with the reference composition indicated above, and thus make it possible to significantly retard preignition, in particular LSPI, in the course of their use in an engine, under conditions simulating aging of the lubricant compositions.

The results in terms of ignition temperature are in particular better when the content of dithiocarbamate compound in the composition is greater than 0.01% by weight.

Example 5: Preparation of the Lubricant Compositions

The lubricant compositions C1 and C2, in accordance with the invention, were prepared.

Their kinematic viscosity at 100° C. was determined according to the standard ISO 3104.

The details of the compositions are presented in Table 7 below, in which the proportions of the various compounds are indicated as mass percentages.

TABLE 7 Composition C1 C2 Base oil Group III/IV 71.8 72.6 Additive package* 15.7 15.7 Viscosity index enhancer of hydrogenated 10.5 10.5 styrene/isoprene copolymer type Diphenylamine antioxidant (Irganox ® L-57) 0.8 0.8 Polymethacrylate 0.2 0.2 MoDTC (Sakuralube ® 525 from Adeka) 0 0 mDTC (Vanlube ® 7723 from Vanderbilt) 1 0 Trimeric MoDTC (Infineum ® C9455B from Infineum) 0 0.2 KV100 (mm²/s) 11.6 11.53 *The additive package is a mixture of different additives that are common in the field of lubricants and commercially available. It comprises wear-resistance additives of zinc dithiophosphate type, detergents based on calcium and magnesium, and dispersants of PIBSI type.

The compositions are prepared by mixing, at a temperature of the order of 30 to 40° C., of the compounds detailed in Table 7.

The lubricant compositions thus prepared have kinematic viscosity values at 100° C. that are suitable for their use in engines, in particular vehicle engines.

The lubricant compositions are subsequently aged according to the protocol (aging method) detailed above.

Example 6: Evaluation of the Lubricant Compositions

The exothermic reaction initiation temperature (ignition temperature) was measured for each of the lubricant compositions of Example 3, according to the measurement method (laboratory preignition tendency method) defined above.

The stability of each of the lubricant compositions was also evaluated according to the protocol (stability measurement) defined above.

The results are given in Table 8 below.

TABLE 8 Ignition Composition temperature [° C.] Stability C1 (Invention) 214 Good stability C2 (Invention) 211 Good stability

Compositions C1 and C2 according to the invention are stable and have ignition temperatures that are higher than that measured for the reference composition, thus making it possible to significantly retard preignition, in particular LSPI, in the course of their use in an engine, under conditions simulating aging of the lubricant compositions. 

1-15. (canceled)
 16. A method for preventing and/or reducing preignition in a vehicle engine, the method comprising contacting the engine with a lubricant composition in the course of at least one oil change interval without adding fresh lubricant composition, the lubricant composition comprising: (i) at least one dithiocarbamate compound; and (ii) at least one base oil; wherein the lubricant composition comprises dithiocarbamate compounds in an amount less than or equal to 1% by weight, relative to the total weight of the lubricant composition.
 17. The method of claim 16, wherein the dithiocarbamate compound is chosen from metal dithiocarbamates, bisdithiocarbamates, or mixtures thereof.
 18. The method of claim 16, wherein the lubricant composition comprises dithiocarbamate compounds in an amount ranging from 0.02% to 1% by weight, relative to the total weight of the composition.
 19. The method of claim 16, wherein the base oil is chosen from the oils of group III, the oils of group IV, or mixtures thereof.
 20. The method of claim 16, wherein the lubricant composition further comprises at least one antioxidant additive different from the at least one dithiocarbamate compound.
 21. The method of claim 20, wherein the at least one antioxidant additive is present in an amount ranging from 0.05% to 2% by weight, relative to the total weight of the lubricant composition.
 22. The method of claim 16, wherein the lubricant composition further comprises at least one detergent additive chosen from alkaline-earth metal salts.
 23. The method of claim 16, wherein the lubricant composition comprises at least one viscosity index-enhancing additive chosen from hydrogenated or non-hydrogenated homopolymers or copolymers, styrene, butadiene, or isoprene.
 24. The method of claim 23, wherein the composition comprises from 2% to 15% by weight of viscosity index-enhancing additive, relative to the total weight of the composition.
 25. A method for preventing and/or reducing preignition in a vehicle engine, the method comprising adding at least one dithiocarbamate compound to a lubricant composition comprising at least one base oil, wherein the lubricant composition is used in the course of at least one oil change interval without adding fresh lubricant composition.
 26. A method for limiting the degradation of performance in terms of preventing and/or reducing preignition in a vehicle engine of a lubricant composition comprising at least one base oil, after its use in the course of at least one oil change interval without adding fresh lubricant composition, the method comprising adding at least one dithiocarbamate compound to a lubricant composition.
 27. A method for increasing the ignition temperature, measured by high-pressure differential scanning calorimetry, of a lubricant composition comprising adding at least one dithiocarbamate compound to said lubricant composition, said composition being used in the course of at least one oil change interval without adding fresh lubricant composition, relative to a spent lubricant composition free of any dithiocarbamate compound.
 28. A process for preventing and/or reducing preignition in a vehicle engine, comprising: a) contacting the engine with a lubricant composition comprising at least one base oil and at least one dithiocarbamate compound, wherein the lubricant composition comprises dithiocarbamate compounds in an amount less than or equal to 1% by weight, relative to the total weight of the lubricant composition; and b) running the engine in the course of at least one oil change interval, without adding fresh lubricant composition.
 29. The process as claimed in claim 28, wherein the dithiocarbamate compound is chosen from metal dithiocarbamates, bisdithiocarbamates, or mixtures thereof.
 30. A method for preventing and/or reducing preignition in a vehicle engine, comprising at least a step of contacting the engine with a lubricant composition comprising: (i) at least one dithiocarbamate compound; and (ii) at least one base oil; wherein the lubricant composition has undergone iron-catalyzed oxidation at a temperature ranging from 150° C. to 170° C. for a time ranging from 120 hours to 150 hours, according to the GFC Lu-43A-11 method.
 31. The method of claim 16, wherein the lubricant composition is contacted with the engine over a distance travelled by the vehicle ranging from 10,000 km to 30,000 km, without adding fresh lubricant composition.
 32. The method of claim 16, wherein the dithiocarbamate compound is chosen from molybdenum dithiocarbamate, methylene bis(dibutyldithiocarbamate), or mixtures thereof.
 33. The method of claim 16, wherein the content of dithiocarbamate compound ranges from 0.1% to 0.5% by weight, relative to the total weight of the composition.
 34. The method of claim 20, wherein the antioxidant additive is chosen from diphenylamine, phenols, phenol esters, or mixtures thereof.
 35. A method for preventing and/or reducing low-speed preignition in a vehicle engine of a motor vehicle, the method comprising contacting the engine with a lubricant composition in the course of at least one oil change interval without adding fresh lubricant composition, the lubricant composition comprising: (i) at least one dithiocarbamate compound; and (ii) at least one base oil; wherein the lubricant composition comprises dithiocarbamate compounds in an amount less than or equal to 1% by weight, relative to the total weight of the lubricant composition. 